1. Field of the Invention
The present invention relates to a magnetic recording medium, method for producing the same, and a method for recording and reproducing magnetic recording information on a thin film type magnetic recording medium having a recording layer consisting of a thin film consisting mainly of a ferromagnetic material. More specifically, the present invention relates to a novel magnetic recording medium and recording and reproduction method, allowing stable magnetic recording and reproduction over a long period of use.
2. Description of the Related Arts
Recently, there is an increasing demand for high density recording. As a substituent for conventional coated type magnetic recording media using a binder, there have been proposed thin film type magnetic recording media in which the recording layer consists of a metal- or oxide-thin film such as a ferromagnetic metal thin film or a cobalt-based alloy thin film having perpendicular magnetic anisotropy as described in, for example, Japanese Examined Patent Publication No. 58-91. However, these magnetic recording layers consisting of such metal- or oxide-thin film have difficulties in that they are subjected to abrasion or damage due to their high frictional resistance against a magnetic recording head, and thus exhibit poor durability.
In order to eliminate this defect, various attempts have been heretofore proposed to further use a protective layer made of organic polymers, high hardness metals, ceramics, etc..
U.S. Pat. No. 3,460,968 discloses protection of the cobalt-containing ferromagnetic thin film, by oxidizing the surface of a thin film so as to convert the Co-containing material to Co.sub.3 O.sub.4. The Co-containing material is exposed to oxidizing atmosphere (air), having for example, a relative humidity of 80-100%, at a temperature of from approximately 40.degree. C. to 150.degree. C. for a period of time of 3 hours or longer. The pure oxygen is also used as the oxidizing atmosphere. In this case, the relative humidity is 80%, the temperature is 43.5.degree. C., and the exposing time is 2 hours.
Japanese Unexamined Patent Publication No. 58-41439 discloses a magnetic recording medium which comprises a polymer base, a thin film of ferromagnetic metal containing Co, and a protective layer containing at least CoO and Co.sub.3 O.sub.4. The ferromagnetic material containing Co is exposed to a glow discharge atmosphere, to form the protective layer. The protective layer is formed by oxidizing only the surface of magnetic layer. The protective layer containing both CoO and Co.sub.3 O.sub.4 is allegedly superior to the layer containing only either CoO or Co.sub.3 O.sub.4 in the light of stability and wear resistance.
Japanese Unexamined Patent Publication No. 58-208935 describes a disadvantage, wherein an oxide layer naturally formed by the oxidation of ferromagnetic metal thin film in the air causes the reduction in the coercive force, squareness ratio and the recording density of the ferromagnetic metal thin film. In order to prevent the reduction in the coercive force and the like, Japanese Unexamined Patent Publication No. 58-208935 proposes a preliminary oxidation, that is, an intentional oxidation of the ferromagnetic material thin film, prior to its oxidation by air. A preliminary exposure to plasma is disclosed. The vacuum deposition is used for forming the protective layer consisting cobalt oxide or nickel oxide on the magnetic layer.
U.S. Pat. No. 4,124,736 discloses a method of protection by a successive formation of a non-metallic barrier layer and an oxide layer on the magnetic recording alloy.
The proposals in the above patent documents are directed to improvement of the abrasion resistance of the above-mentioned thin film type magnetic recording medium, i.e., the life of the magnetic recording medium, since when it is repeatedly run on a magnetic recording head, the life is inferior to that of conventional magnetic recording media of coated type. Nevertheless, the prior arts do not succeed in improvement of the abrasion resistance, so that the thin film type magnetic recording medium can be applied for the commercial magnetic recording and reproducing system, since the durability attained by the prior arts does not exceed, for example, more than 1,000,000 passes of the floppy disc. In other words, if the protection methods of the prior art are applied for the thin film type magnetic recording medium, the medium must be replaced before 1,000,000 passes have been made.
Also, as a magnetic recording head for conventional coated type magnetic recording media, there are known those in which the surface in sliding contact with the recording medium is composed of barium titanate, and the like. In the sliding operation for recording and reproduction, these magnetic recording heads do not mar the medium and has excellent durability, since the sliding surface of the head itself is not abraded. However, unlike the above-mentioned coated type medium impregnated with a lubricant or the like to enhance its durability, the above-mentioned thin film type magnetic recording medium comprises a recording layer consisting of a metal thin film incapable of being impregnated with a lubricant. Therefore, when the magnetic recording head is brought into sliding contact with the thin film type recording medium, the head is liable to be damaged, and conversely, this damage of the head is likely to mar the recording-medium.
The prior art of magnetic heads for use in recording and regenerating the signal in the thin film recording medium include Japanese Unexamined Patent Publications Nos. 50-3615, 57-117117, 58-139323, 59-151322, 59-71112, and, 58-35717 and U.S. Pat. No. 4251841. In the last of the above publications, the support for the main poles is a polycrystalline sintered body mainly composed of alumina and titanium carbide (AlTiC), and the thin film recording medium to be used in contact with the magnetic head is a sputtered Co-Cr film.